Part of an object having an indentation or curving inwards.

### Examples

- The graph of the second-degree polynomial function defined by the equation
*f*(*x*) =*a*x² is concave upward when the coefficient a has a positive value and concave downward when the coefficient*a*has a negative value. The figure below shows the function*f*defined by*f*(*x*) = 0.5(*x*+ 4)2 − 3, in which parameter*a*= 0.5 is positive. Therefore, the graph is concave upward.

- A lune is a plane concave figure that is bounded by two circular arcs with unequal radii.